1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus to prevent sheets from running into an idle roller during a discharge of special sheets.
2. Description of the Related Art
Referring to FIG. 1, a conventional image forming apparatus is provided with a sheet supply cassette 11 in which sheets are stacked on a lower end of a body 10. The sheets in the sheet supply cassette 11 are picked up one after another by a pickup roller 12. The picked up sheets are sent to a developing portion 13. The developing portion 13 includes a photosensitive drum 14, a developing roller 15 and a transfer roller 16. The photosensitive drum 14 is charged with an electric potential by a charging device, and an electrostatic latent image corresponding to a predetermined image is formed on a charged surface by light scanned from a laser scanning unit 17. The electrostatic latent image area is fed with toner supplied by the developing roller 15. Accordingly, an image is formed and then transferred to and printed on a sheet passing between the photosensitive drum 14 and the transfer roller 16.
The sheet with the printed image is fixed at an elevated temperature and under a high pressure through a fixing portion 18, so that the toner image is fused thereonto. After passing through the fixing portion 18, the sheet passes through first, second and third sheet feeding rollers 21, 22 and 23 one after another, and is then stacked on a sheet stacking surface 10a provided on an upper section of the body 10. First, second and third idle rollers 24, 25 and 26 are further provided to rotatably contact with the sheet feeding rollers 21, 22 and 23, respectively, and thus rotate together to pass the sheet.
To print on both sides of the sheet, after passing the first or second sheet feeding roller 21 or 22, the sheet is reversed and directed through a duplex feeding path 30 to be fed again.
When a special sheet like an envelope, OHP film, etc., is printed by the above image forming apparatus, the sheet is discharged from the body 10 right after being passed through the first sheet feeding roller 21 in order to reduce an occurrence of a jam, curl, etc. Here, the second sheet feeding roller 22 and the second idle roller 25 are not used for sheet feeding. In other words, during special sheet printing, a rear cover 19 of the body 10 is opened with an angle from about 40° to 60°, as shown in FIG. 1. Then, the sheet is stacked on an inner guiding ribbed-surface 19a of the rear cover 19.
In the above-described construction, the second idle roller 25 protrudes higher than the guiding ribbed-surface 19a. Therefore, during the stacking of a sheet discharged from the body 10, there is a possibility that a leading end of the sheet may run into the idle roller 25, and thus change direction. Furthermore, there may be difficulty in stacking sheets due to sheet bending.